Effect Of Fertilization On Growth And Mortality Of Jack Pine Growing On Poor, Sandy Soils In Michigan, Usa: Implications For Sustainable Management

Our understanding of nutrient limitations to jack pine (Pinus banksiana Lamb.) growth is lacking across the Lake States of the USA (Michigan, Wisconsin and Minnesota), where this species makes up an important forest cover type on nutrient poor sands. Currently this cover type is managed using whole-tree harvesting (WTH) across large areas of state and federal forestland, which raises concerns for long-term declines in soil fertility and future productivity. In this study, I carried out a factorial fertilization experiment to better understand potential nutrient limitations to jack pine growth on excessively drained sandy soils in northern Lower Michigan. Treatments were nitrogen (N), phosphorus (P) and base cations applied singly and in all factorial combinations. In addition, I constructed input-output nutrient budgets for jack pine management in northern Lower Michigan using existing data on atmospheric deposition, weathering and harvest nutrient removals. In no case did I observe an increase in tree growth rate to fertilization, instead I observed an overall decline in growth rates, and an increase in mortality rates, in trees fertilized with N. Nitrogen-induced imbalances of foliar N: potassium (K) were strongly correlated with decreased growth in N amended plots. Together with nutrient budget analysis, which indicated that harvest removals of K greatly exceed inputs over the planned rotation, this suggests that WTH may not be sustainable over multiple rotations. Furthermore, the impacts of WTH on ecosystem K status are likely to be exacerbated over time by anthropogenic N deposition.